Impact of meteorological and geographical factors on the distribution of Phlebotomus chinensis in northwestern mainland China

Identification of bio-climatic determinants and potential risk areas for Kyasanur forest disease in Southern India using MaxEnt modelling approach

BACKGROUND

Kyasanur forest disease (KFD), known as monkey fever, was for the first time reported in 1957 from the Shivamogga district of Karnataka. But since 2011, it has been spreading to the neighbouring state of Kerala, Goa, Maharashtra, and Tamil Nadu. The disease is transmitted to humans, monkeys and by the infected bite of ticks Haemaphysalis spinigera. It is known that deforestation and ecological changes are the main reasons for KFD emergence, but the bio-climatic understanding and emerging pathways remain unknown.

METHODS

The present study aims to understand the bio-climatic determinants of distribution of tick vector of KFD in southern India using the Maximum Entropy (MaxEnt) model. The analysis was done using 34 locations of Haemaphysalis spinigera occurrence and nineteen bio-climatic variables from WorldClim. Climatic variables contribution was assessed using the Jackknife test and mean AUC 0.859, indicating the model performs with very high accuracy.

RESULTS

Most influential variables affecting the spatial distribution of Haemaphysalis spinigera were the average temperature of the warmest quarter (bio10, contributed 32.5%), average diurnal temperature range (bio2, contributed 21%), precipitation of wettest period (bio13, contributed 17.6%), and annual precipitation (bio12, contributed 11.1%). The highest probability of Haemaphysalis spinigera presence was found when the mean warmest quarter temperature ranged between 25.4 and 30 °C. The risk of availability of the tick increased noticeably when the mean diurnal temperature ranged between 8 and 10 °C. The tick also preferred habitat having an annual mean temperature (bio1) between 23 and 26.2 °C, mean temperature of the driest quarter (bio9) between 20 and 28 °C, and mean temperature of the wettest quarter (bio8) between 22.5 and 25 °C.

CONCLUSIONS

The results have established the relationship between bioclimatic variables and KFD tick distribution and mapped the potential areas for KFD in adjacent areas wherein surveillance for the disease is warranted for early preparedness before the occurrence of outbreaks etc. The modelling approach helps link bio-climatic variables with the present and predicted distribution of Haemaphysalis spinigera tick.

An investigation of the effects of environmental and ecologic factors on cutaneous leishmaniasis in the old world: a systematic review study

OBJECTIVES

Leishmaniasis is a neglected and widespread parasitic disease that can lead to serious health problems. The current review study aimed to synthesize the relationship between ecologic and environmental factors (e.g., weather conditions, climatology, temperature and topology) and the incidence of cutaneous leishmaniasis (CL) in the Old World.

CONTENT

A systematic review was conducted based on English, and Persian articles published from 2015 to 2020 in PubMed/Medline, Science Direct, Web of Science and Google Scholar. Keywords used to search articles were leishmaniasis, environmental factors, weather condition, soil, temperature, land cover, ecologic* and topogr*. All articles were selected and assessed for eligibility according to the titles or abstracts. The quality screening process of articles was carried out by two independent authors. The selected articles were checked according to the inclusion and exclusion criteria.

SUMMARY AND OUTLOOK

A total of 827 relevant records in 2015-2020 were searched and after evaluating the articles, 23 articles met the eligibility criteria; finally, 14 full-text articles were included in the systematic review. Two different categories of ecologic/environmental factors (weather conditions, temperature, rainfall/precipitation and humidity) and land characteristics (land cover, slope, elevation and altitude, earthquake and cattle sheds) were the most important factors associated with CL incidence.

CONCLUSIONS

Temperature and rainfall play an important role in the seasonal cycle of CL as many CL cases occurred in arid and semiarid areas in the Old World. Moreover, given the findings of this study regarding the effect of weather conditions on CL, it can be concluded that designing an early warning system is necessary to predict the incidence of CL based on different weather conditions.

Distribution of Suitable Environments for Phlebotomus chinensis as the Vector for Mountain-Type Zoonotic Visceral Leishmaniasis - Six Provinces, China

What is already known on this topic?

Phlebotomus chinensis(P. chinensis) is a sandfly and the main vector of mountain-type zoonotic visceral leishmaniasis (MT-ZVL) in China. However, the distribution of suitable environments for the vector has not been studied yet.

What is added by this report?

This study found that temperate hilly zones in midwestern China are suitable for P. chinensis survival with appropriate environmental factors such as moderate normalized difference vegetation value (NDVI), land use type, landform, temperature, and vegetation. Suitable living conditions for the high-density P. chinensis that caused the reemergence of MT-ZVL already existed.

What are the implications for public health practice?

Targeted strategies should be implemented to control the vector and the reemergence of MT-ZVL, such as by strengthening key environment monitoring and taking accurate measures for residents, mobile and migrant populations.

Spatial analysis and epidemiological profile of visceral leishmaniasis, northeastern Brazil: A cross-sectional study

Most visceral leishmaniasis (VL) cases reported in Brazil are from the northeast region, where the disease is strongly linked to poverty. In spite of the still existing inequalities, many social improvements were achieved in the past decades in this region, but the possible impact of these improvements on VL remains poorly investigated. We conducted a cross-sectional study coupled with a spatial analysis of VL cases notified in northeastern Brazil from 2007 to 2017. In total, 21,703 cases were reported during this period, with an annual incidence of 3.6 cases per 100,000 inhabitants. Children under 10 years old and males were more affected, and most cases were from urban areas. Living in municipalities situated in the Cerrado, Amazon or, to a lesser extent, in the Caatinga biomes was a risk factor for VL. This study indicates that the epidemiological profile of VL patients remained unchanged in northeastern Brazil, suggesting that social improvements achieved in this region were not enough to mitigate the risk of this disease among the most affected populations.

Modelling the potential distribution of arbovirus vector Aedes aegypti under current and future climate scenarios in Taiwan, China

BACKGROUND

Aedes aegypti is one of the most important mosquito species and is a common disease-transmitting pest in tropical areas. Various infectious arbovirus diseases can be transmitted by Ae. aegypti. With ongoing global climate change, we are facing an increasing public health threat from the rapid spread of disease vectors into wider geographical areas. To better understand the current ecological niche range and possible future expansion of Ae. aegypti, an ecological niche modelling approach was adopted to predict its current and future potential habitat in Taiwan, China.

RESULTS

Based on observed occurrence records and environmental layers reflecting climate and land-use conditions, predictions with a high resolution of 30 arcsec (approx. 1 × 1 km) were made by our model. Ae. aegypti was predicted to expand its habitat in varying degrees out of its current niche range under different climate scenarios for the future 21st century. Winter temperature and dry season precipitation were considered as important predictors among climate variables. Croplands, pasture, forested lands and urban lands were important land-use variables.

CONCLUSION

Ae. aegypti is expected to establish new habitats out of its current niche range under the trend of global climate change. The extent of habitat expansion varies under different climate scenarios. Appropriate measures should be taken to prevent its expansion to a broader scale. Our study has important strategic implications for mosquito surveillance and the prevention and control of mosquito-borne diseases. © 2019 Society of Chemical Industry.

Modeling the present and future distribution of arbovirus vectors Aedes aegypti and Aedes albopictus under climate change scenarios in Mainland China

Aedes aegypti and Aedes albopictus are two important mosquito species which transmit various infectious arbovirus diseases represented mainly by dengue fever. These two species of mosquito have a wide range of distribution and strong transfer capacity. With ongoing global climate change, we are facing an increasing public health threat from the rapid spread of vectors in wider geographical areas. Based on observed occurrence records of Ae. aegypti and Ae. albopictus and high-resolution environmental layers reflecting climate and land-use conditions, a Maxent niche modeling approach was adopted to model the current and future distribution of both species in Mainland China. Our models provide predictions of suitable habitat shifts under future climate scenarios up to the 2050s. Both species were predicted to expand their niche range to varying degrees under future climate scenarios. Aedes aegypti was modeled to expand its habitat from Guangdong, Guangxi, Yunnan and Hainan to Fujian, Jiangxi and Guizhou. Aedes albopictus was modeled to increase magnitude of distribution within its present range of northern, southwestern and southeastern coastal areas of Mainland China. Area and population exposed to mosquitoes are predicted to increase significantly. Environmental variables that have significant impact on the distribution of mosquitoes are also revealed by our model. The results of our study can be referenced in further ecological studies and will guide the development of strategies for the prevention and control of mosquito-borne diseases.